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TIHIEMEASUREMENTO FTRANSIENT2圃 D PROFILESO FVELOCITV A N DFUELCONCENTRATIONOVERLlQUIDS
AkihikoIto OitaUniversity
GassanTashtoush UniversityofKentucky
AkiraNarumi KanagawaInstituteofTechnology
KozoSaito UniversityofKentucky
TadashiKonishi OitaUniversity
ClifordJ.Cremers UniversityofKentucky
ABSTRACT Werecentlydevelopedtwodiferentopticaltechniquesinorder
tosimultaneouslymeasuretransient2-Dprofilesofvelocity，tempera- tureandfuelconcentrationthatweregeneratedbyaspreadingflame overliquidfue1s. Onetechniqueemploysapartic1e-tracksystemcom- binedwithalaser-shetsystem(PTLS)andahighspedcamera，whi1e theothertechniqueemploysadualwavelengthholographicinterfer- ometry(DWHI). ThePTLSsystemrevealedtransient2・D profilesof flameinducedflow，whileDWHIrevealed2-Dprofilesofuelconcerト trationoverliquids. Inthispaperwepresentaseriesofvelocitypro- filesforapulsatingflamespreadoverpropanolandconcentrationpro- filesforgaseouspropanoldeterminedwithPTLSandDWHIrespec- tively. Otherresearchershavepredictedtheformationofsmaltwin circulations，oneagas-phasecirculationjustaheadoftheflame'slead- ingedge，andtheotherasmaliquidcirculationjustunderneaththe gas-phasecirculation. OurPTLSresultsconfirmedthesepredictions， .ie.，theformationof5-10milimeterdiametercirculationinthegas phaseandanaccompanyingaproximately20milimeterdiameterliq- uidcirculation. Basedonthesedata，weoferaphe~omenological ex- planationofthemechanismofpulsatingflamespread. Inadition，we showthatDWHIisaverypromisingtechniqueformeasuringtransient fuel-concentrationprofilesoverliquids.
iNTRODUCTION
HistoricalBacl(around Thephenomenonofflamespreadoverliquidsisofcurentinter-
estbecauseofitsimportancetofiresafety. Ourobjectiveisdiferen.t Wewishtolearnmoreaboutthefundamentalmechanismoftheflame spread.Anexcelentreviewoftheliteratureonthisproblemwaspub- lishedbyRoss[194]出ldHiranoandSuzuki[193]andthetheoretト calbackgroundoftheproblemwasprovidedbyWil1iams[1985].They adresedmanyoftheproblemsthatnededtobeinvestigated.
Thepresentpaperisacontinuationofourpreviousstudiesonflame spreadoverliquids[lto，Masuda，Saito，191;Ito，Saito，andCremers， 195;andTashtoush，Narumi，lto，Saito，andCremers，196].Inthese
studiesweapliedholographicinterferometry(HI)toobtainadetailed andinstantaneoustemperaturedistributionintheliquidphasenearthe fuelsurface. Ineachofmethanol，ethanolandpropanolwefoundsub- surface-liquidconvectioninboththeuniformspread，andpulsating spreadregions.Tounderstandthemechanismsofflamespreadinboth regions，researcherstriedtoidentifythem司orheat-transferproces betweentheflame'sleadingedgeandtheliquid，whetheritocurs t h r o u g h t h e g a s p h a s e ， 1i q u i d p h a s e 0 1' b o t h . W h e n t h e i i q u i d c o n v e c - tionisproducedandittravelsaheadoftheflame'sleadingedge，the t1amespreadislikelytobecontroledbyitbecausetheconvection cariesthehightemperatureliquidaheadoftheflame'sleadingedge. Thisenhancesevaporationofliquidvaporresultingintheformationof aflamablemixtureofuelandairthroughwhichtheflamecanspread. Ifthereisnoliquidconvectionaheadoftheflame'sleadingedge，the majo1'heattransfercanocurbetwentheflame'sleadingedgeandthe liquidbyconductionandradiationinthegasphase，becauseconduc- tionthroughtheliquidisnegligible[GlasmanandDryer，1981].
Liquidconvectionisuniquetoflamespreadoverliquidsandit complicatesthespreadingprocesincomparisontoflamespreadover solids，whichhavenocondensedphaseconvection[Wi1liams，1985]. Thus，itisimportanttomeasuretemperatureandvelocityprofilesin theliquidphase. Akita[1972]wasthefirstresearchertoaplya shadowgraphtechniquetovisualizethe1iquidconvection. Hereported theformationofliquidconvectioninthepulsatingregion，butnoliquid convectionintheuniformspreadregion. BasedonAkita'sdata， GlassmanandDryer[1981]proposedthattheuniformspreadiscon- troledbyheatconductionthroughthegasphase，whileinthepulsating regiontheliquidconvectionplaysanimportantrole. However，the proposedmechanismfortheuniformspreadisquestionable，because thegas-phaseconductionmaynottransfersu百Icientheatforthef1ame tospreadatarateofnearly10cm/s.
Tosolvethisproblem，wedevelopedanHIsystemandperformed thetransientmeasurementof1iquidtemperature[1:10，Masuda，andSaito， 191].TheresponsetimeofourHIsystemislesthan1microsecond. Weestimatetheuncertaintyofthespatialresolutiontobe(0.1m m，